There is no direct way to do this. The closest is to search a Key number text such as NRSVS for the word@[KEY G...]. Then search the tagged text for [CONTENTS NRSVS] <AND> your specific form. You can then weed out any false positives.

I was hoping that was not the case. It might work with more distinctive words, but with an "if" there will be a lot of false positives. Since there is the ability with appropriate text modules to see cross-hi-lighting of equivalent forms, it ought to be possible to design relevant cross-module searches like this. It would certainly be worth adding to the list of potential features.

Rod,
I felt like playing around with what you were trying to do. Humor me and see if this is what you are looking for. Using the ESVS, I came up with a list of 25 verses that contain participial phrases which contain the English word "if."

My Greek is not as seasoned as yours (I am still in seminary), so I looked up "conditional dependent verbal participles" in Wallace's grammar (p. 632) to get an idea about what was meant. I noticed that in his examples there was not a Greek word for "if".
So, I searched:
1) The ESVS: if @ -[KEY*]
This gave me 107 hits where "if" was not connected to a Greek word, and must be a part of the English translation.
2) I added the GNT-T and copied all of the Greek verses to a reference list.
3) I created a new search using the GNT-T: [verb participle] <and> [CONTENTS ref list]
This gave me 50 verses.
4) I thought that was suitable enough to read through and weed out the false positives. I couldn't think of a way to filter it down any more, and it only took a few minutes using the interlinear to spot the bad ones.

*Wallace gives other examples of these conditional participles, but the ones I have listed above are specific to the "if" request.